You can't prove a negative. There's really no way to prove Mars didn't have or doesn't have life.

Which definitely doesn't mean we shouldn't look or go.

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Chris Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

You can't prove a negative. There's really no way to prove Mars didn't have or doesn't have life.

Which definitely doesn't mean we shouldn't look or go.

You can't prove a negative, but you can end up assigning something a high probability of not being the case. You can also rephrase the question in such a way so that the absence of lie becomes a positive statement, e.g.

The hypotheses that there is life on Mars or that Mars is abiogenic are not simple hypotheses but bundles of inter-connected hypotheses, with testing happening in parallel. We have to avoid being naively Popperian in our methodology.

Remember that even now, after decades of work, not everyone is convinced that there was life on the Archean Earth. Although there almost certainly was, IMHO.

"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

Remember that even now, after decades of work, not everyone is convinced that there was life on the Archean Earth. Although there almost certainly was, IMHO.

The explosive (not really, but you know what I mean) march of life across the early Earth really does imply lots of viable precursors/attempts/follies or even panspermia here and elsewhere. Even in the 'simple' early times, it looks like things were never simple or early! The implication of the surprisingly fast spread of life in the not terribly nice early Earth environment is that it also kicked off elsewhere whenever it could - but remember that 'life' need not be more than highly evolved and rather efficient slime with becoming a stromatolite as a career objective...

Remember that even now, after decades of work, not everyone is convinced that there was life on the Archean Earth. Although there almost certainly was, IMHO.

The explosive (not really, but you know what I mean) march of life across the early Earth really does imply lots of viable precursors/attempts/follies or even panspermia here and elsewhere. Even in the 'simple' early times, it looks like things were never simple or early! The implication of the surprisingly fast spread of life in the not terribly nice early Earth environment is that it also kicked off elsewhere whenever it could - but remember that 'life' need not be more than highly evolved and rather efficient slime with becoming a stromatolite as a career objective...

Nice way of putting it. But don't forget evidence of life is rare in rocks older than 3 Ga, uncommon in rocks 1.8-3 Ga, and it isn't until after about 1.8 Ga that it becomes geologically common. You can traverse kilometres of geological section in Archean rocks and not find any evidence of life.

"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

Remember that even now, after decades of work, not everyone is convinced that there was life on the Archean Earth. Although there almost certainly was, IMHO.

The explosive (not really, but you know what I mean) march of life across the early Earth really does imply lots of viable precursors/attempts/follies or even panspermia here and elsewhere. Even in the 'simple' early times, it looks like things were never simple or early! The implication of the surprisingly fast spread of life in the not terribly nice early Earth environment is that it also kicked off elsewhere whenever it could - but remember that 'life' need not be more than highly evolved and rather efficient slime with becoming a stromatolite as a career objective...

Nice way of putting it. But don't forget evidence of life is rare in rocks older than 3 Ga, uncommon in rocks 1.8-3 Ga, and it isn't until after about 1.8 Ga that it becomes geologically common. You can traverse kilometres of geological section in Archean rocks and not find any evidence of life.

Is there abundant evidence for life in metamorphosed rock from the most recent billion years?

Remember that even now, after decades of work, not everyone is convinced that there was life on the Archean Earth. Although there almost certainly was, IMHO.

The explosive (not really, but you know what I mean) march of life across the early Earth really does imply lots of viable precursors/attempts/follies or even panspermia here and elsewhere. Even in the 'simple' early times, it looks like things were never simple or early! The implication of the surprisingly fast spread of life in the not terribly nice early Earth environment is that it also kicked off elsewhere whenever it could - but remember that 'life' need not be more than highly evolved and rather efficient slime with becoming a stromatolite as a career objective...

Nice way of putting it. But don't forget evidence of life is rare in rocks older than 3 Ga, uncommon in rocks 1.8-3 Ga, and it isn't until after about 1.8 Ga that it becomes geologically common. You can traverse kilometres of geological section in Archean rocks and not find any evidence of life.

Is there abundant evidence for life in metamorphosed rock from the most recent billion years?

Mid-greenschist facies rocks can show fossils, sedimentary and volcanic structures, some biomarkers, and sometimes, original isotopic signatures, such as these from the Pilbara WA (stromatolites and pillow lavas).

"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

NASA must avoid spreading Earth microbes to suspected water in hillside streaks.

Quote

Curiosity is currently about 5 kilometres away from the potential RSLs; on its current projected path, it would never get any closer than about 2 kilometres, Vasavada says. The rover could not physically drive up and touch the streaks if it wanted to, because it cannot navigate the slopes of 25 degrees or greater on which they appear.

But the roverís sheer unexpected proximity to potential RSLs has NASA re-evaluating its planetary-protection protocols. Curiosity was only partly sterilized before going to Mars, and experts at JPL and NASA headquarters in Washington DC are calculating how long the remaining microbes could survive in Marsís harsh atmosphere ó as well as what weather conditions could transport them several kilometres away and possibly contaminate a water seep. ďThat hasnít been well quantified for any mission,Ē says Vasavada.

US society is getting way too paranoid about "safety" and "protection" of just about anything.

I take it you're not a biologist? I am, and I can guarantee you it is not possible to be too paranoid when it comes to contamination of biological samples.

Yes it is, if it prevents you from doing the work.

And what exactly would the purpose be of doing work that is potentially flawed to the point of being worse than doing nothing? In the world of sciences, it is generally best to avoid gathering data that is flawed or of which the accuracy is uncertain (hence possibly contaminated biological samples).

Gathering such data can indeed often be better than nothing and allow for some hypotheses to be evaluated beyond reasonable doubt, but in some cases (life sciences in particular) it is more likely to lead one astray then to benefit them scientifically.

US society is getting way too paranoid about "safety" and "protection" of just about anything.

I take it you're not a biologist? I am, and I can guarantee you it is not possible to be too paranoid when it comes to contamination of biological samples.

Yes it is, if it prevents you from doing the work.

No it isn't. If you can't guarantee your samples aren't pure, there literally is no point in taking them. It the same as a surgeon saying "I can't be too paranoid about the sterility of my scalpel, as that means I can't operate". If there isn't a good enough guarantee the scalpel is sterile, the surgery is off. This is exactly the same. If they can't guarantee the sterility of MSLs instruments, there is no point in sampling.

In the world of sciences, it is generally best to avoid gathering data that is flawed or of which the accuracy is uncertain (hence possibly contaminated biological samples).

It's not ever as clear cut as that. Time and again flawed datasets with large uncertainties have been revisited, sometimes decades later, with new analysis methods, cross referencing and complementary newer data etc.

US society is getting way too paranoid about "safety" and "protection" of just about anything.

I take it you're not a biologist? I am, and I can guarantee you it is not possible to be too paranoid when it comes to contamination of biological samples.

Yes it is, if it prevents you from doing the work.

And what exactly would the purpose be of doing work that is potentially flawed to the point of being worse than doing nothing? In the world of sciences, it is generally best to avoid gathering data that is flawed or of which the accuracy is uncertain (hence possibly contaminated biological samples).

Gathering such data can indeed often be better than nothing and allow for some hypotheses to be evaluated beyond reasonable doubt, but in some cases (life sciences in particular) it is more likely to lead one astray then to benefit them scientifically.

What makes you think the data is so flawed as to be worse than doing nothing? Its hard to think of a scenario in this case where this would be the case?

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"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

In the world of sciences, it is generally best to avoid gathering data that is flawed or of which the accuracy is uncertain (hence possibly contaminated biological samples).

It's not ever as clear cut as that. Time and again flawed datasets with large uncertainties have been revisited, sometimes decades later, with new analysis methods, cross referencing and complementary newer data etc.

Classic example being the Pathfinder APXS data.

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"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

US society is getting way too paranoid about "safety" and "protection" of just about anything.

I take it you're not a biologist? I am, and I can guarantee you it is not possible to be too paranoid when it comes to contamination of biological samples.

Yes it is, if it prevents you from doing the work.

And what exactly would the purpose be of doing work that is potentially flawed to the point of being worse than doing nothing? In the world of sciences, it is generally best to avoid gathering data that is flawed or of which the accuracy is uncertain (hence possibly contaminated biological samples).

Gathering such data can indeed often be better than nothing and allow for some hypotheses to be evaluated beyond reasonable doubt, but in some cases (life sciences in particular) it is more likely to lead one astray then to benefit them scientifically.

What makes you think the data is so flawed as to be worse than doing nothing? Its hard to think of a scenario in this case where this would be the case?

It's very easy to do that; where contaminations aren't recognised as such and give you false positives.

US society is getting way too paranoid about "safety" and "protection" of just about anything.

I take it you're not a biologist? I am, and I can guarantee you it is not possible to be too paranoid when it comes to contamination of biological samples.

Yes it is, if it prevents you from doing the work.

And what exactly would the purpose be of doing work that is potentially flawed to the point of being worse than doing nothing? In the world of sciences, it is generally best to avoid gathering data that is flawed or of which the accuracy is uncertain (hence possibly contaminated biological samples).

Gathering such data can indeed often be better than nothing and allow for some hypotheses to be evaluated beyond reasonable doubt, but in some cases (life sciences in particular) it is more likely to lead one astray then to benefit them scientifically.

What makes you think the data is so flawed as to be worse than doing nothing? Its hard to think of a scenario in this case where this would be the case?

It's very easy to do that; where contaminations aren't recognised as such and give you false positives.

Which is why people in this case would work carefully with the data to minimise the problem. We know how clean the rover was when launched, we have ultraclean experimental blanks for the SAM suite, we can model the effects of more than four years (probably six or more by the time they get there) exposure to the martian environment.

« Last Edit: 09/11/2016 04:15 AM by Dalhousie »

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"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres